Various types exist in the reclining apparatus, for example, there has been suggested an internal gear type reclining apparatus as described in Japanese Patent Application Laid-Open No. 7-231820. The internal gear type reclining apparatus is, as one embodiment thereof is shown in FIG. 18, provided with a fixed plate 3 having a pair of guide convex portions 1 and 2 opposing to each other, a slide gear 4 received between the guide convex portions 1 and 2, a rotary plate 6 having an internal gear 5, a cam member 7 and the like. The cam member 7 can be rotated in a direction of an arrow A in FIG. 18 (a lock canceling direction) by an operating lever 8. The fixed plate 3 is fixed to a frame in a seat cushion side. The rotary plate 6 is fixed to a frame in a seat back side and can rotate around a shaft 9 integrally together with the seat back.
A gear teeth portion 10 freely engaged with and disengaged from the internal gear 5 is formed in a front end portion of the slide gear 4. When the slide gear 4 is pressed toward the internal gear 5 by a cam surface 11 of the cam member 7, the gear teeth portion 10 is engaged with the internal gear 5 so as to be in a lock condition, whereby the rotary plate 6. That is, the seat back is fixed at a desired angle.
An engaging portion 13 engaging with a receiving portion 12 of the slide gear 4 is formed in the cam member 7. When the operating lever 8 is rotated in a clockwise direction and the slide gear 4 is driven in a direction moving apart from the internal gear 5 by the engaging portion 13, an engagement between the slide gear 4 and the internal gear 5 is canceled and the lock thereof is canceled, so that the rotary plate 6. That is, the seat back can rotate around the shaft 9.
In the reclining apparatus (FIG. 18) mentioned above, at a time of adjusting an angle of incline of the seat back in a condition that a passenger sits on the seat, a load (a backward load) of an upper half of the sitting person is applied to the seat back. In this case, since the front end portion of the slide gear 4 is going to rotate in a direction shown by an arrow R1 integrally together with the rotary plate 6 in a condition that the slide gear 4 is engaged with the internal gear 5 as shown in FIG. 19, a clockwise moment M1 is applied to the slide gear 4. The slide gear 4 is tilted due to the moment M1, and the slide gear 4 becomes in a condition of being pressed to a contact point B near a corner in a base end side of one guide convex portion 1 and a contact point C near a corner in front end side of another guide convex portion 2.
In this condition, when the engaging portion 13 of the cam member 7 is rotated in a clockwise direction by rotating the operating lever 8 in a lock canceling direction as shown in FIG. 20, a force f1 in a direction moving the slide gear 4 apart from the internal gear 5 is applied to the receiving portion 12 of the slide gear 4. However, since the force f1 generates a moment further tilting the slide gear 4 in a clockwise direction, the contact pressure in the contact points B and C is further increased, so that a great lock canceling force is required for operating the operating lever 8. Accordingly, the sitting person operates the operating lever 8 so as not to apply so much load to the seat back, and it is difficult to operate.
In the case of assuming a rear-end collision, or the like, in the lock condition in FIG. 18, a great input is applied in a direction shown by an arrow R1 in FIG. 19, whereby the moment M1 applied to the slide gear 4 is further increased. Accordingly, the contact force in the contact points B and C is further increased. Accordingly, in an engaging portion 15 close to the front end of the guide convex portion 2, a gap G between the gear teeth portion 10 and the internal gear 5 tends to be increased as shown in FIG. 21. As a result, the engaging efficiency between the slide gear 4 and the internal gear 5 is reduced, and it is difficult to ensure the engaging strength and the engaging rigidity. Accordingly, it is necessary to employ countermeasures such as increasing the gear teeth thickness or increasing the number of gear teeth. However, there is a limit for increasing the thickness of the gear teeth and the number of the gear teeth, and it causes increase of the whole size of the reclining apparatus.
Furthermore, in a reclining apparatus described in Japanese Patent Application Laid-Open No. 8-52040, a flange of a bracket formed in a shape obtained by vertically notching a hat is fixed to a fixed plate, an inner peripheral side end portion of a spiral spring is engaged with a notched cylindrical portion of the bracket, and an outer peripheral side end portion thereof is engaged with a pin fixed to a rotary plate. In this case, the bracket is positioned by fitting two holes formed in the flange to a convex portion formed in the fixed plate, and is fixed to the fixed plate by welding the flange to the fixed plate. Furthermore, the pin is fixed to the rotary plate by being inserted into a through hole formed in the rotary plate and thereafter caulking an inserted end.
Furthermore, in the reclining apparatus, the following structure is employed so that the fixed plate and the rotary plate slide with each other in a circumferential direction. That is, a circular recess step portion is formed in a center portion of one plate and a convex step portion fitting into the recess step portion is formed in a center portion of another plate, whereby both elements can relatively rotate around an axis. Furthermore, a plurality of pins having flanges are caulked and fixed to one plate, and the flanges of the pins prevent the outer peripheral portion of the end surface of another plate from moving in an axial direction. Accordingly, both plates relatively rotate in a circumferential direction in a condition of being in contact with each other.
Furthermore, it is necessary to provide a limit in a tilt range of the seat back. For example, in Japanese Patent Application Laid-Open No. 11-56510, there is disclosed an arrangement structured such that by forming an elongated through hole formed in a circular arc shape in one plate and fixing a pin inserted into the elongated through hole to another plate, the pin is brought into contact with the end portion of the elongated through hole and a seat back does not tilt more than the contact portion.
In the arrangement disclosed in Japanese Patent Application Laid-Open No. 8-52040, since the bracket engaged with the inner peripheral side end portion of the spiral spring is substantially formed in a hat, a space occupied by the flange of the bracket is increased, and there is a problem that the size of the bracket is increased. Furthermore, since the bracket is fixed by welding the edge portion of the flange to the fixed plate, the distance between the welded portion of the bracket and the cylindrical portion to which the load due to the spiral spring is applied is increased. Accordingly, in order to prevent a deformation between the welded portion and the cylindrical portion, it is necessary to increase a thickness of the bracket, so that there is a problem that not only the weight of the reclining apparatus is increased but also the 1 material cost and the working cost are increased.
Furthermore, a restricting means for the rotary plate using the elongated through hole and the pin inserted thereto is employed in many reclining apparatuses in addition to the structure disclosed in Japanese Patent Application Laid-Open No. 11-56510. However, since a pin exclusive for restricting a rotation is required, there is a problem that a number of the parts is increased.
Furthermore, as described in Japanese Patent Application Laid-Open No. 8-52040, in the arrangement for preventing another plate from relatively moving in the axial direction by the pin having the flange, at least three pins are required in view of a structural stability. However, there is a requirement to make the number of the parts as small as possible.
Furthermore, as described in Japanese Patent Application Laid-Open No. 8-52040, in the arrangement in which the convex step portion is fitted into the recess step portion so as to slide the fixed plate and the rotary plate in the circumferential direction, a contact area of the both is great, and a frictional resistance is increased due to burrs formed at a time of press punching, so that there may be a problem in which the seat back does not smoothly tilt. On the contrary, when a gap is formed between the fixed plate and the rotary plate, dusts enter into the sliding portion and a resistance in rotation is increased.
In general, the reclining apparatus is exerted with a load which is input via the seat back from a back portion of the sitting person, and the back frame carries the load within the seat back. A mounting portion of the reclining apparatus is mounted to the back frame by means of welding or bolts, and is directly supported to an upper rail of the seat slide or indirectly supported via a cushion frame. The load of the sitting person applied to the back frame is naturally applied to the reclining apparatus. However, the load is mainly applied to an engaging portion between the rotary plate and the fixed plate, that is, the engaging portion between the gear teeth portion of the slide gear and the internal gear.
In this case, a relational formula of the load in the reclining apparatus as mentioned above is shown as follows.
As shown in FIG. 22A, on the assumption that the load applied to the seat back is defined as “F”, the distance from the center of rotation of the seat back to the point of application is defined as “L”, the radius of the pitch circle between the slide gears 1a and 1b and the gear teeth portion of the internal gear 2 is defined as “r”, the reaction force generated due to the engagement between the upper slide gear 1a and the internal gear 2 is defined as “fa”, and the reaction force generated due to the engagement between the lower slide gear 1b and the internal gear 2 is defined as “fb”, the following formula is obtained on the basis of balance of force.F+fb=fa 
The following formula is obtained on the basis of balance of moment.F×L=(fa+fb)×r The following formulas are obtained on the basis of two formulas mentioned above.fa=(L+r)×F/2r fb=(L−r)×F/2r  (1) 
Accordingly, the load applied to the engaging position between the slide gears 1a and 1b and the internal gear 2 is different between upper and lower portions, and it is known that the load applied to the upper slide gear 1a is larger than the load applied to the lower slide gear 1b. Accordingly, the strength of the upper slide gear 1a must be higher than the strength of the lower slide gear 1b. This matter can be applied to the guide portion of the slide gears 1a and 1b. However, in an actual condition, two kinds of slide gears having different strength designs are not manufactured in order to simplify manufacturing operations or assembling operations. Furthermore, when the parts of the slide gears are made common as mentioned above, the strength design is made so as to cope with the upper load condition having a great load. This results in unnecessary increase of the thickness or the size in the slide gear arranged in the lower side, and results in increase of the size or the weight in overall the apparatus.
Furthermore, generally, in a condition in which the slide gear and the internal gear are engaged with each other, a back-lash is inevitably formed by the clearance for the engagement between the both gears. The back-lash is instantaneously formed when the sitting person leans against the seat back, however, if there is a difference in the load applied to the slide gear as mentioned above, there is a case in which the back-lash is formed two times at every engaging positions. FIGS. 23A ad 24A are graphs showing a condition in which the back-lash is formed. FIG. 23A shows a condition in which a load is applied to the seat back, whereby at first a back-lash is formed at the upper engaging position to which a great load is applied (a portion shown by reference symbol g1), and next back-lash (a portion shown by reference symbol g2) according to a small load application is formed at the lower engaging position. FIG. 24A simply shows a displacement of the seat back with respect to the case in which a load is applied to the seat back, and a parallel portion shown by reference symbols g1 and g2 shows a formation of the back-lash. As mentioned above, when the back-lash is formed in two stages, the sitting person feels discomfort and unpleasant sensation although these senses may be instantaneous, so that this is a problem to be improved.
In the reclining apparatus mentioned above, there is provided with a holding member for guiding rotation of the rotary plate and preventing both of the plates from breaking away from each other. The holding member has a pin and a flange fixed to the front end portion of the pin. For example, in the reclining apparatus disclosed in Japanese Patent Application Laid-Open Nos. 7-136032 and 7-231820, the holding member is provided in both plates one by one, and is arranged so as to slidably hold an outer peripheral portion of an opposing plate between its own plate and the flange.
In the reclining apparatus mentioned above, when the sitting person leans against the seat back and the load is applied to the seat back, the load is transmitted to the engaging position between the slide gear and the internal gear via the rotary plate. Therefore, a force breaking away both of the plate from each other is generated between the fixed plate and the rotary plate around the engaging position. Actually, it is possible to prevent the plates from breaking away by the holding member. However, there is a problem in which since the holding member provided in the rotary plate side naturally moves together with the rotary plate, the relative position between the holding member and the engaging position changes according to the angle of tilt of the seat back, and the elements sometimes move greatly apart from each other. That is, the holding member in the rotary plate side largely moves away from the engaging position at which the force breaking both of the plates away from each other is generated. Accordingly, the holding force applied by the holding member is not effectively applied to the engaging position, so that the engaging force is reduced. Therefore, the sizes of the holding member, the slide gear and the like are increased so as to ensure the strength thereof, and overall the apparatus has disadvantages in which the size and the weight thereof increase.
A first object of the present invention is to provide a reclining apparatus which can increase an engaging strength between an internal gear and a slide gear in the case of assuming a rear-end collision or the like.
A second object of the present invention is to provide a reclining apparatus which requires a small operating force at a time of canceling a lock and has an improved operability.
A third object of the present invention is to reduce material cost and working cost as well as making a bracket engaged with an inner peripheral side end portion of a spiral spring compact and thin so as to achieve weight saving.
A fourth object of the present invention is to achieve restriction of rotation of a rotary plate and restriction of movement in an axial direction against a fixed plate by reduced number of parts.
A fifth object of the present invention is to ensure tight contact between the fixed plate and the rotary plate so as to reduce frictional resistance between the both while preventing dusts from entering.
A sixth object of the present invention is to achieve compact design and weight saving, and improvement of strength while it is a matter of course to commonly use parts in a slide gear. A seventh object of the present invention is to reduce a back-lash generated at an engaging position between a slide gear and an internal gear.
An eighth object of the present invention is to provide a reclining apparatus which can effectively restrict a force applied so that a rotary plate tends to break away from a fixed plate without relation to a position of the rotary plate, as a result, can increase an engaging force between the slide gear and the internal gear so as to achieve compact design and weight saving, and improvement of strength.